Sheet stacking apparatus, method for controlling sheet stacking apparatus, and storage medium

ABSTRACT

A sheet stacking apparatus includes a lowering control unit, a determination unit, and a control unit. The lowering control unit lowers a sheet stacking unit according to a stacked sheet amount. The determination unit determines whether the sheet stacking unit cannot be lowered by the lowering control unit. The control unit performs control to store a position of the sheet stacking unit and stop stacking of the sheet when the determination unit determines that the sheet stacking unit cannot be lowered while the sheet is being stacked on the sheet stacking unit. The control unit performs control to raise the sheet stacking unit when the stacked sheet is removed in a state where the stacking of the sheet on the sheet stacking unit is stopped, stack the sheet on the raised sheet stacking unit, and stop lowering of the sheet stacking unit based on the stored position.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a sheet stacking apparatus that can stack sheets on a sheet stacking unit, a method for controlling the sheet stacking apparatus, and a storage medium.

2. Description of the Related Art

Conventionally, a sheet stacking apparatus that discharges a sheet onto an elevatable sheet stacking unit has been available.

The sheet stacking apparatus, after an image is printed on a sheet, discharges the sheet on which the image is printed, onto the sheet stacking unit through a discharge port. Every time the sheet is discharged onto the sheet stacking unit, the sheet stacking unit is lowered so that the uppermost surface of the sheets stacked on the tray is positioned adjacent to the discharge port. Thus, the sheet discharged from the discharge port can be stably stacked.

When an obstacle that hinders lowering of the sheet stacking unit is placed below the sheet stacking unit, the sheet stacking unit being lowered bumps on the obstacle. Here, when an attempt to further lower the sheet stacking unit that has bumped on the obstacle is made, a load is imposed on a driving unit for lowering the sheet stacking unit. Thus, the sheet stacking unit and the driving unit might break.

In view of such an occasion, the following technique has been known. When the operation of lowering the sheet stacking unit is hindered by the obstacle, the operation of discharging the sheet and the operation of lowering the sheet stacking unit are stopped and a warning is displayed (Japanese Patent Application Laid-Open No. 2001-226022).

In a case of the conventional technique, after the warning is displayed, a user calls a serviceman to release the warning. The warning can be released only when the maintenance by the serviceman is completed.

Thus, it is preferable that the operation of stacking the sheet can be performed within a moveable range of the sheet stacking unit after the sheet stacked on the sheet stacking unit, which has bumped on the obstacle, is removed by the user. When the operation of stacking the sheet can be performed within the moveable range of the sheet stacking unit, the sheet stacking unit might bump on the obstacle again and thus the sheet stacking unit and the driving unit of the sheet stacking unit might break under the imposed load.

SUMMARY OF THE INVENTION

According to an aspect of the present invention, a sheet stacking apparatus includes a lowering control unit configured to lower a sheet stacking unit according to an amount of a sheet that is stacked, a determination unit configured to determine that the sheet stacking unit cannot be lowered by the lowering control unit, and a control unit configured to perform control to store a position of the sheet stacking unit in a storage unit and stop stacking of the sheet on the sheet stacking unit when the determination unit determines that the sheet stacking unit cannot be lowered while the sheet is being stacked on the sheet stacking unit, wherein the control unit is configured to perform control to raise the sheet stacking unit when the sheet stacked on the sheet stacking unit is removed in a state where the stacking of the sheet on the sheet stacking unit is stopped, stack the sheet on the raised sheet stacking unit, and stop lowering of the sheet stacking unit based on the position stored in the storage unit.

In a sheet stacking apparatus, an operation of discharging a sheet to a sheet stacking unit can be performed after lowering of the sheet stacking unit is hindered by an obstacle while a risk is reduced that the sheet stacking unit is broken. Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating a configuration of an image processing apparatus according to an exemplary embodiment.

FIG. 2 is a cross-sectional view illustrating the configuration of the image processing apparatus according to the exemplary embodiment.

FIG. 3 is a diagram for describing an operation unit according to the exemplary embodiment.

FIG. 4 is a flowchart for describing a control example according to exemplary embodiment.

FIG. 5 is a flowchart for describing a control example according to exemplary embodiment.

FIG. 6 is a flowchart for describing a control example according to exemplary embodiment.

FIG. 7 is a flowchart for describing a control example according to the exemplary embodiment.

FIG. 8 is a diagram for describing a screen according to the exemplary embodiment.

FIG. 9 is a diagram for describing a screen according to the exemplary embodiment.

FIG. 10 is a diagram for describing a screen according to the exemplary embodiment.

FIG. 11 is a diagram for describing a screen according to the exemplary embodiment.

FIG. 12 is a cross-sectional view of an image processing apparatus according to another exemplary embodiment.

FIG. 13 is a flowchart for describing a control example according to the other exemplary embodiment.

DESCRIPTION OF THE EMBODIMENTS

Various exemplary embodiments, features, and aspects of the invention will be described in detail below with reference to the drawings.

A first exemplary embodiment will be described below. FIG. 1 is a diagram illustrating a printing system according to the present exemplary embodiment. The printing system according to the present exemplary embodiment includes a personal computer (PC) 111 and a multifunctional peripheral (MFP) 100 as an example of a sheet stacking apparatus.

The MFP 100 according to the present exemplary embodiment includes a control unit 110, a reader unit 200, and a printer unit 300. The sheet stacking apparatus, which is exemplarily described as the MFP in the present exemplary embodiment, may also be a single function peripheral (SFP) as long as a printing function of the printer unit 300 is provided. The reader unit 200, the control unit 110, and the printer unit 300 are electrically connected with each other, and transmit and receive a control command and data to and from each other. A discharging unit 330 is detachably attached to the MFP 100.

The control unit 110 includes a central processing unit (CPU) 120, an image memory 130, a nonvolatile memory 140, a random access memory (RAM) 150, a read only memory (ROM) 160, an operation unit 170, and a timer 180.

The CPU 120 loads a program stored in the ROM 160 onto the RAM 150 and executes the program to comprehensively control the MFP 100.

The RAM 150 functions as a work area for the CPU 120, and stores various programs and data.

The ROM 160 stores the various programs loaded and executed by the CPU 120.

The image memory 130 is a memory that stores image data. For example, the image memory 130 stores image data read by the reader unit 200 and image data received from the PC 111. The image data stored in the image memory 130 is transmitted to the printer unit 300 in accordance with an instruction from the CPU 120.

The nonvolatile memory 140 serves as a storage unit that holds data without power supply. The nonvolatile memory 140 stores various programs and the image data. The nonvolatile memory 140 may be in any form such as a hard disk drive (HDD), a digital versatile disk (DVD), a solid state drive (SDD), and a Blu-ray disk, as long as there is an enough capacity to store the image data.

The operation unit 170 includes a display section and hard keys. The operation unit 170 displays an operation screen and receives an operation from a user.

The timer 180 is used to measure time.

A network interface (I/F) 190 controls the MFP 100 to communicate with an external apparatus such as the PC 111 via a network. The external apparatus, which is described as the PC 111 herein, may be another MFP, a mobile terminal, or a facsimile apparatus. In the present exemplary embodiment, an example where the MFP 100 and the external apparatus are connected to each other through a wired network 112 is described. Alternatively, the MFP 100 and the external apparatus may be connected with each other through a universal serial bus (USB) cable. Furthermore, the MFP 100 and the external apparatus may communicate with each other through wireless communications such as Wi-Fi.

The reader unit 200 includes a scanner unit 210 and a document feed unit (DF unit) 250. The scanner unit 210 reads an image on a document and generates image data representing a read image. The DF unit 250 feeds the document to be read by the scanner unit 210.

The printer unit 300 is a unit for printing an image onto a sheet (recording paper). The printer unit 300 feeds the sheets stored in a sheet feeding unit 310 one at a time to convey to a marking unit 320. The sheet feeding unit 310 includes cassettes 311 to 314 and a manual feed tray 315.

The marking unit 320 prints an image onto the sheet thus fed, based on the image data transmitted from the image memory 130. The marking unit 320 may employ electrophotography or inkjet printing. The marking unit 320 may employ any other methods with which an image can be printed.

The printer unit 300 conveys the sheet, on which the image has been printed, to the discharging unit 330. The discharging unit 330 includes a stack tray 507, and discharges the sheet thus conveyed to the stack tray 507. The stack tray 507 is one example of a sheet stacking unit and is also referred to as a discharge tray. A CPU 591 controls the discharging unit 330 in accordance with an instruction from the CPU 120. FIG. 1 shows a case where the discharging unit 330 includes the CPU 591, but the CPU 591 is not necessarily required. The CPU 120 may issue an instruction directly to a motor drive control unit 562. An example where the CPU 120 directly controls the discharging unit 330 is described below. An elevation motor 561 is a motor for raising and lowering the stack tray 507. The motor drive control unit 562 is a control unit for driving the elevation motor 561. The stack tray 507 is raised by a normal rotation of the elevation motor 561, and is lowered by a reverse rotation of the elevation motor 561. The motor drive control unit 562 operates in accordance with the instruction from the CPU 120. A tray detection sensor 571 is a sensor for detecting a position (height) of the stack tray 507. A sheet presence sensor 581 is a sensor for detecting the presence of the sheet stacked on the stack tray 507. A height detection sensor 582 is a sensor for detecting a height of the sheets stacked on the stack tray 507.

Next, the MFP 100 described in FIG. 1 is described in detail by referring to FIG. 2.

The document feed unit 250 in the reader unit 200 feeds documents set on a document positioning plate one at a time to convey to an optical unit 213. The document conveyed to the optical unit 213 is discharged onto a discharge tray 219.

When the document is conveyed to a portion above the optical unit 213, the reader unit 200 activates a lamp 212, and the optical unit 213 irradiates the document with light. The light reflected from the document is guided to a charge coupled device (CCD) image sensor (hereinafter, referred to as CCD) 218 by mirrors 214, 215, and 216 and a lens 217. Thus, the image on the document is read by the CCD 218. Image data output from the CCD 218 is subjected to predetermined processing, and then is transmitted to the control unit 110.

The reader unit 200 also reads an image on a document placed between the DF unit 250 and a platen glass 211. In this case, the reader unit 200 activates the lamp 212 and moves the optical unit 213. The light reflected from the document is guided to the CCD 218 by the mirrors 214, 215, and 216 and the lens 217. Thus, the image on the document is read by the CCD 218. Image data output from the CCD 218 is subjected to predetermined processing, and then is transmitted to the control unit 110. The case where the image on the document is read by the CCD 218 is described in the present exemplary embodiment. Alternatively, the image on the CCD 218 may be read by a contact image sensor (CIS). When the image on the document is read by the CIS, the mirrors 214, 215, and 216, as well as the lens 217 are not required, and the CIS is disposed at the position of the optical unit 213.

In the printer unit 300, a laser driver 321 drives a laser emitting unit 322. Specifically, the laser driver 321 causes the laser emitting unit 322 to emit a laser beam corresponding to the image data output from the image memory 130 of the control unit 110. The laser beam is radiated onto a photosensitive drum 323. Thus, a latent image corresponding to the laser beam is formed on the photosensitive drum 323. A development device 324 makes a developer attached on the portion of the photosensitive drum 323 where the latent image is formed.

The printer unit 300 includes, as the sheet feeding unit 310, the cassettes 311 to 314 in a form of a drawer and the manual feed tray 315. The printer unit 300 feeds the sheet from any one of the cassettes 311 to 314 and the manual feed tray 315, and conveys the sheet to a transfer unit 325 through a conveyance path 331. The transfer unit 325 transfers the developer attached to the photosensitive drum 323, onto the sheet.

The sheet on which the developer has been transferred is conveyed to a fixing unit 327 by a conveyance belt 326. The fixing unit 327 fixes the developer on the sheet with heat and pressure. Then, the sheet that has passed through the fixing unit 327 is discharged through a conveyance path 335 and a conveyance path 334. When the sheet is discharged with the print side reversed, the sheet is guided to a conveyance path 338 through a conveyance path 336. Then, the sheet is conveyed in a reverse direction and can be conveyed through a conveyance path 337 and the conveyance path 334.

When two-sided printing is set, the sheet that has passed through the fixing unit 327 passes through the conveyance path 336, and then is guided to a conveyance path 333 by a flapper 329. Then, the sheet is conveyed in the reverse direction, guided to the conveyance path 338 by the flapper 329, and then is guided to a refeeding conveyance path 332. The sheet guided to the refeeding conveyance path 332 passes through the conveyance path 331 at the timing described above, and is conveyed to the transfer unit 325. Here, a surface on which an image has been transferred beforehand by the transfer unit 325 is defined as a first surface. The transfer unit 325 transfers the developer onto a second surface different from the first surface. Then, the sheet is guided to the conveyance path 334 through the fixing unit 327.

The sheet conveyed through the conveyance path 334 is conveyed to the discharging unit 330, regardless of whether the one-sided printing or the two-sided printing is set.

The sheet conveyed to the discharging unit 330 is first conveyed to a buffer unit 501 where buffering is performed when required. When the buffering is performed, the conveyed sheet is rolled around a buffer roller. If it takes time to perform processing such as stapling on the downstream side, the buffer unit 501 can be used to adjust conveying interval of the sheet transmitted from the main body.

Then, the sheet is conveyed by a pair of upstream discharge rollers 502 and a pair of downstream discharge rollers 503 through a conveyance path 504 to be stacked on a stack tray 505. When a single copy of sheets is stacked on the stack tray 505, the sheet stack is discharged onto the stack tray 507.

When shifting is instructed, the sheet stack on the stack tray 505 is discharged onto the stack tray 507 while being shifted by 1 cm from a previously discharged sheet stack. Thus, the user can easily recognize the segments between the copies. The sheet shifting distance may be greater or less than 1 cm.

When stapling is instructed, a staple unit 506 performs staple processing on the sheets conveyed by the pair of upstream discharge rollers 502 and the pair of downstream discharge rollers 503 through the conveyance path 504 to stack the sheets on the stack tray 505. The sheet stack thus bound is discharged onto the stack tray 507 by the pair of downstream discharge rollers 503.

The stack tray 507 is fixed to a belt 554. The belt 554 is stretched between an upper pulley 551 and a lower pulley 552. The belt 554 has concavity and convexity and is stretched with the concavity and convexity meshing with concavity and convexity of the upper pulley 551 and of the lower pulley 552. Thus, the belt 554 moves in accordance with a movement of the upper pulley 551. The upper pulley 551 rotates in clockwise and counterclockwise directions in FIG. 2, when the elevation motor 561 illustrated in FIG. 1 is driven. Specifically, when the elevation motor 561 rotates in a normal direction, the upper pulley 551 rotates in the clockwise direction in FIG. 2, whereby the stack tray 507 is raised by the belt 554 that moves in accordance with the upper pulley 551. When the elevation motor 561 rotates in a reverse direction, the upper pulley 551 rotates in the counterclockwise direction in FIG. 2, whereby the stack tray 507 is lowered by the belt 554 that moves in accordance with the upper pulley 551. The lower pulley 552 moves in accordance with the movement of the belt 554 without receiving power from the elevation motor 561. Alternatively, the lower pulley 552 may also be moved by the power received from the elevation motor 561.

The height detection sensor 582 is a sensor for measuring a distance to the upper surface of the stack tray 507 or a distance to an upper surface of the stacked sheets. Specifically, when no sheet is stacked on the stack tray 507, the upper surface of the stack tray 507 is irradiated with infrared light, and an amount of the reflected infrared light is detected and measured. Thus, the distance to the upper surface of the stack tray 507 is measured. When the sheet is stacked on the stack tray 507, the upper surface of the sheet is irradiated with infrared light, and an amount of the reflected infrared light is detected and measured. Thus, the distance to the upper surface of the sheet is measured. The CPU 120 control the elevation motor 561 to lower the stack tray 507 or to raise the stack tray 507, to maintain a constant distance to the upper surface of the stack tray 507 or the upper surface of the sheet. Specifically, the stack tray 507 is lowered or raised in accordance with the number of sheets stacked on the stack tray 507. When the sheet is discharged, the stack tray 507 is lowered. The stack tray 507 is raised when the sheet on the stack tray 507 is removed.

The sheet presence sensor 581 is a sensor that detects the presence of the sheet stacked on the stack tray 507. Specifically, the sheet on the stack tray 507 is detected by detecting whether a switch protruding above the stack tray 507 is pressed down by the weight of the sheet. The weight of a single sheet is heavy enough to press down the switch. The sheet presence sensor 581 transmits to the CPU 120, a signal indicating the presence of a sheet when there is a sheet on the stack tray 507, and a signal indicating the absence of the sheet when there is no sheet. The CPU 120 receives the signal from the sheet presence sensor 581, and determines whether there is a sheet on the stack tray 507.

A plurality of the tray detection sensors 571 is disposed to detect the position of the stack tray 507. The CPU 120 detects the position of the stack tray 507, by checking which tray detection sensor 571 is detecting the discharge tray.

An upper end sensor 573, which is the uppermost one of the tray detection sensors 571, is disposed at a position of the stack tray 507 raised as much as possible, and thus detects that the stack tray 507 is at the highest position (uppermost position). A lower end sensor 574, which is the lowermost one of the tray detection sensors 571, is disposed at a position of the stack tray 507 lowered as much as possible, and thus detects that the stack tray 507 is at the lowest position (lowermost position).

Next, the operation unit 170 of the MFP 100 illustrated in FIG. 1 will be described by referring to FIG. 3.

The operation unit 170 includes a key input section 601 that receives a user operation through hard keys and a touch panel section 602 that can display soft keys and receives a user operation through the soft keys.

The key input section 601 is first described. The key input section 601 includes an operation unit ON/OFF switch 603. When the user presses the operation unit ON/OFF switch 603 when the MFP 100 is in a standby mode (normal power mode), the CPU 120 switches the MFP 100 from the standby mode to a sleep mode (a mode consuming less power than in the normal power mode). When the user presses the operation unit ON/OFF switch 603 when the MFP 100 is not in the sleep mode, the CPU 120 switches the MFP 100 from the sleep mode to the standby mode.

A start key 605 is a key for receiving an instruction to cause the MFP 100 to execute copying and data transmission from the user.

A stop key 604 is a key for receiving an instruction to stop the copying and the data transmission from the user.

Ten keys 606 are used by the user to set the register number for various settings.

Next, the touch panel section 602 will be described. The touch panel section 602 includes a liquid crystal display (LCD section) and a touch panel sheet formed of a transparent electrode attached on the LCD. The touch panel section 602 has a function of displaying an operation screen and receiving various settings from the user and a function of notifying the user of a state of the MFP 100, an error message, or the like. In the present exemplary embodiment, an example where the operation unit 170 includes both the touch panel section 602 and the key input section 601 is described. The present invention is not limited to this example. For example, the operation unit 170 may not include the key input section 601 and include the touch panel section 602 only. The touch panel section 602 may display keys having the same function as the keys in the key input section 601 as needed.

The MFP 100 having the configuration described above can execute various types of jobs.

For example, the MFP 100 executes a copy job of reading an image on a document, generating image data representing the image on the document, and printing the image onto a sheet based on the image data and a setting received through the operation unit 170.

The MFP 100 executes a print job of analyzing print data received from the PC 111, generating image data based on a print setting received from the PC 111, and printing an image onto a sheet based on the generated image data.

The MFP 100 executes a fax print job of receiving code data from an external facsimile apparatus through a phone line, converting the received code data into image data, and printing an image onto a sheet based on the image data obtained by the conversion.

The MFP 100 receives a plurality of the jobs, sequentially stores the jobs in the nonvolatile memory 140, and sequentially executes the jobs from the oldest job to the newest job stored in the nonvolatile memory 140.

Here, the configuration where the MFP 100 executes a plurality of types of jobs is described. However, the present invention is not limited to this, and the MFP 100 may be capable of executing some of the plurality of types of jobs.

Every time the sheet is discharged onto the stack tray 50, the CPU 120 of the MFP 100 detects the upper surface of the sheet with the height detection sensor 582 and drives the elevation motor 561 to lower the stack tray 507. Thus, sheet discharge failure due to the jamming of the discharge port by the sheets discharged onto the stack tray 507, can be prevented. The stack tray 507 is raised or lowered so that the uppermost surface of the sheet is positioned adjacent to the discharge port. Thus, there is an advantage that the sheet discharged through the discharge port can be stably stacked. In the present exemplary embodiment, an example where the stack tray 507 is lowered every time a single sheet is discharged is described. Alternatively, the stack tray 507 may be lowered every time a stack of a predetermined number of sheets, not smaller than two, is discharged. For example, the stack tray 507 may be lowered every time 10 sheets are discharged.

When the obstacle that hinders the lowering of the stack tray 507 is placed below the elevatable stack tray 507 as shown in FIG. 12, the stack tray 507 bumps on the obstacle and cannot be lowered any further. An attempt to further lower the stack tray 507 might break the stack tray 507 and the elevation motor 561 due to the load imposed on the stack tray 507 and the elevation motor 561.

Thus, if the tray detection sensor 571 detects that the position of the stack tray 507 is unchanged even when the elevation motor 561 is driven, the CPU 120 determines that there is an obstacle below the stack tray 507, and thus stops the printing and stops lowering the stack tray 507. Then, the CPU 120 displays an obstacle detection error on the operation unit 170.

Thus, the stack tray 507 and the elevation motor 561 can be prevented from breaking due to the attempt to lower the stack tray 507 despite the presence of the obstacle.

When the user, who sees the obstacle detection error displayed on the operation unit 170, calls the serviceman and stops the printing until the serviceman comes, the printing cannot be executed for a long period of time.

Thus, in the present exemplary embodiment, the CPU 120 starts raising the stack tray 507 upon detecting that the sheet stacked on the stack tray 507 is removed after the obstacle detection error occurs. Then, the CPU 120 resumes the printing, and thus the sheet is discharged onto the stack tray 507 and the stack tray 507 is gradually lowered. Thus, the productivity can be prevented from degrading.

When the print documents are stacked on the stack tray 507 again thereafter, the stack tray 507 is gradually lowered to bump on the obstacle again. Thus, the stack tray 507 and the elevation motor 561 are likely to be broken under the imposed load. The load imposed on the stack tray 507 and the elevation motor 561 increases as the number of times the stack tray 507 bumps on the obstacle increases, so that the risk of breaking the stack tray 507 and the elevation motor 561 increases.

Thus, in the present exemplary embodiment, when it is detected that the stack tray 507 has bumped on the obstacle and thus cannot be lowered any further, the position of the stack tray 507 at that point is stored. Thus, when the stack tray 507 is lowered again, lowering of the stack tray 507 is stopped at the stored position. Accordingly, the productivity can be prevented from degrading and a risk of breaking the stack tray 507 becomes lower.

Next, the control performed by the CPU 120 according to the present exemplary embodiment will be described by referring to flowcharts in FIGS. 4 to 7. The CPU 120 performs processing illustrated in the flowcharts in FIGS. 4 to 7 by loading a program stored in the ROM 160 onto the RAM 150 and executing the program.

In step S1010, the CPU 120 determines whether a job involving printing is stored in the nonvolatile memory 140. The processing proceeds to step S2020 when the CPU 120 determines that such a job is stored. The processing in step S1010 is repeated when the CPU 120 determines that such a job is not stored. Examples of the job involving printing include the copy job, the print job, and the fax print job described above.

In step S1020, the CPU 120 feeds a sheet from any one of the cassettes 311 to 314 and the manual feed tray 315. Then, the CPU 120 controls the marking unit 320 so that an image is printed onto the fed sheet based on the image data and a print setting of the job.

In step S1030, the CPU 120 causes the discharging unit 330 to discharge the sheet onto the stack tray 507.

In step S1040, the CPU 120 causes the height detection sensor 582 to detect the upper surface of the sheet stacked on the stack tray 507. Then, the CPU 120 issues an instruction to the motor drive control unit 562 of the discharging unit 330 to drive the elevation motor 561 so that the stack tray 507 is lowered to maintain a constant distance from the height detection sensor 582 to the upper surface of the sheet stacked on the stack tray 507.

In step S1050, the CPU 120 acquires the position (height) of the stack tray 507 based on a signal transmitted from the tray detection sensor 571.

In step S1060, the CPU 120 determines whether the position of the stack tray 507 is detected by the lower end sensor 574. When the CPU 120 determines that the position of the stack tray 507 is detected by the lower end sensor 574, the tray is full and the processing proceeds to step S1120.

Processing performed in step S1120 is described by referring to FIG. 5.

In step S2010, the CPU 120 issues an instruction to stop the printing to the marking unit 320. Here, the CPU 120 performs control so that the sheet feeding is stopped and an image is printed onto the sheet remaining on the sheet conveyance path and then the sheet is discharged onto the stack tray 507.

In step S2020, the CPU 120 causes the operation unit 170 to display a tray full screen. FIG. 8 illustrates an example of the displayed tray full screen. In FIG. 8, a message indicating that a tray full error has occurred is displayed. Furthermore, a message instructing the user to remove the sheet stacked on the stack tray 507 is displayed. Furthermore, a message indicating that the printing is resumed when the sheet is removed and a message instructing the user to press a cancel key 801 to cancel the printing are displayed. The cancel key 801 is a key for cancelling the job in which the printing is stopped.

In step S2030, the CPU 120 determines whether the sheet is removed from the stack tray 507. The CPU 120 determines that the sheet has not been removed from the stack tray 507, and the processing proceeds to step S2080, as long the sheet stacked on the stack tray 507 is detected by the sheet presence sensor 581. The CPU 120 determines that the sheet has been removed from the stack tray 507 and the processing proceeds to step S2040, when the sheet presence sensor 581 no longer detects the sheet stacked on the stack tray 507.

In step S2080, the CPU 120 determines whether the print cancel instruction is received from the user through the cancel key 801. When the cancel key 801 is pressed, the CPU 120 determines that the print cancel instruction is received from the user, and the processing proceeds to step S2090. When the CPU 120 determines that the cancel key 801 is not pressed, the processing returns to step S2030.

In step S2090, the CPU 120 cancels the job in which the printing has been stopped and deletes information on the job from the nonvolatile memory 140. Then, the processing is terminated.

When the processing proceeds from step S2030 to step S2040, the CPU 120 issues an instruction to drive the elevation motor 561 to the motor drive control unit 562, so that the stack tray 507 is raised.

In step S2050, the CPU 120 determines whether the stack tray 507 has reached an initial position. The processing proceeds to step S2060 when the CPU 120 determines that the stack tray 507 has not reached the initial position, and proceeds to step S1100 in FIG. 4 when the CPU 120 determines that the stack tray 507 has reached the initial position. The initial position is a position where the stack tray 507, on which no sheet is stacked, is placed to receive the discharged sheet. The CPU 120 determines that the stack tray 507 has reached the initial position when the upper end sensor 573 in FIG. 2 detects the stack tray 507.

In S2060, the CPU 120 determines whether an abnormality is detected while the stack tray 507 is being raised. The processing proceeds to step S2070 when the CPU 120 determines that the abnormality is detected, and proceeds to step S2040 when the CPU 120 determines that the abnormality is not detected. For example, the abnormality of the stack tray 507 is detected when the belt 554 is detached from the upper pulley 551 or the lower pulley 552 during an operation of raising the stack tray 507. The abnormality of the stack tray 507 is also detected when the power is not transmitted from the elevation motor 561 to the upper pulley 551. Specifically, the CPU 201 detects the abnormality when the position of the stack tray 507 detected by the tray detection sensor 571 remains unmoved without raising even though the elevation motor 561 is driven in the direction to raise the stack tray 507. In that case, the CPU 201 determines that the abnormality has been detected at the time the stack tray 507 is being raised.

In step S2070, the CPU 120 displays a service error illustrated in FIG. 9 on the operation unit 170, and the processing is terminated. In the screen illustrated in FIG. 9, a message indicating that a repair is required and a message instructing the user to call the serviceman are displayed. Furthermore, the contact information for calling the serviceman is also displayed. A message instructing the user to call an operator and contact information of the operator may be displayed instead of the message instructing the user to call the serviceman and the contact information for calling the serviceman. In other words, the message instructing the user to call the serviceman is not displayed when the stack tray 507, being lowered, bumps on the stack tray 507, and thus cannot be lowered any further. The message is displayed when the stack tray 507, in the course of raising, becomes unable to be raised any further.

Step S1060 in the flowchart in FIG. 4 is described.

The processing proceeds to step S1070 when the CPU 120 determines that the position of the stack tray 507 is not detected by the lower end sensor 574 in step S1060.

In step S1070, the CPU 120 determines whether an abnormality is detected while the stack tray 507 is being lowered. The processing proceeds to step S1110 when the CPU 120 determines that the abnormality is detected, and proceeds to step S1080 when the CPU 120 determines that the abnormality is not detected. For example, the abnormality is detected when lowering of the stack tray 507 is hindered by the obstacle placed below the stack tray 507. Specifically, the CPU 201 detects the abnormality when the position of the stack tray 507 detected by the tray detection sensor 571 remains unmoved without lowering even though the elevation motor 561 is driven in the direction to lower the stack tray 507. In that case, the CPU 201 determines that the abnormality has been detected at the time the stack tray 507 is being lowered.

In step S1110, the CPU 120 determines whether the stack tray 507 is at the initial position. The processing proceeds to step S1130 when the stack tray 507 is not at the initial position, and proceeds to step S1140 when stack tray 507 is at the initial position

The processing proceeds to step S1130 from step S1110, if the amount of sheets that can be stacked on the stack tray 507 is smaller than the maximum amount of sheets that can be stacked on the stack tray 507 in a normal state due to the obstacle placed below the stack tray 507 as illustrated in FIG. 12. Here, the user can decide to remove the obstacle disposed under the stack tray 507 to resume the printing, or remove the sheet stacked on the stack tray 507 without removing the obstacle to resume the printing. The CPU 120 executes processing in step S1130 to enable the user to make such decisions. The processing in step S1130 is described in detail by referring to FIG. 6.

First, the CPU 120 issues an instruction to stop the printing to the marking unit 320. Here, the CPU 120 performs control so that the sheet feeding is stopped. An image is printed onto the sheet remaining on the sheet conveyance path and then the sheet is discharged onto the stack tray 507.

In step S3020, the CPU 120 acquires the position of the stack tray 507 based on the signal from the tray detection sensor 571.

In step S3030, the CPU 120 stores the position of the stack tray 507 thus acquired as the lowering restricted position, in the nonvolatile memory 140. The position of the stack tray 507 is stored by storing information for identifying the tray detection sensor 571 that has detected the stack tray 507 at the point of step S3030, among information pieces for respectively identifying the tray detection sensors 571. In an example illustrated in FIG. 12, the information for identifying a tray full detection sensor denoted by 590 is stored.

In step S3040, the CPU 120 displays a tray full screen with a message instructing the user to remove the obstacle. FIG. 10 illustrates an example of a screen displayed in step S3040. In FIG. 10, a message indicating that the obstacle detection error has occurred is displayed. The message indicating that the printing can be resumed by removing the sheet stacked on the stack tray 507 or the obstacle is displayed. A cancel key 805 is a key for canceling the job in which the printing has been stopped. An OK key 806 is a key pressed by the user after removing the obstacle. The CPU 120 determines that the obstacle is removed upon detecting that the OK key 806 is pressed.

In step S3050, the CPU 120 determines whether the sheet is removed from the stack tray 507. The CPU 120 determines that the sheet has not been removed from the stack tray 507 and the processing proceeds to step S3100 as long as the sheet presence sensor 581 detects the sheet stacked on the stack tray 507. The CPU 120 determines that the sheet has been removed from the stack tray 507 and the processing proceeds to step S3060 when the sheet presence sensor 581 no longer detects the sheet stacked on the stack tray 507.

In step S3100, the CPU 120 determines whether the obstacle is removed based on whether the OK key 806 is pressed. Specifically, the CPU 120 determines whether the OK key 806 illustrated in FIG. 10 is pressed by the user. The processing proceeds to step S3110 when the CPU 120 determines that the OK key 806 is pressed, and proceeds to step S3120 when the CPU 120 determines that the OK key 806 is not pressed.

When the processing proceeds to step S3110, the CPU 120 clears the lowering restricted position stored in the nonvolatile memory 140, and the processing proceeds to step S1100 in FIG. 4.

When the processing proceeds to step S3120, the CPU 120 determines whether the print cancel instruction is received from the user through the cancel key 805. When the cancel key 805 is pressed, the CPU 120 determines that the print cancel instruction is received from the user, and the processing proceeds to step S3130. When the CPU 120 determines that the cancel key 805 is not pressed, the processing returns to step S3050.

In step S3130, the CPU 120 cancels the job with respect to which the printing has been stopped and deletes information on the job from the nonvolatile memory 140. Then, the processing is terminated.

When the processing proceeds to step S3060 from step S3050, the CPU 120 instructs the motor drive control unit 562 to drive the elevation motor 561 so that the stack tray 507 is raised.

In step S3070, the CPU 120 determines whether the stack tray 507 has reached an initial position. The processing proceeds to step S3080 when the CPU 120 determines that the stack tray 507 has not reached the initial position, and proceeds to step S1100 in FIG. 4 when the CPU 120 determines that the stack tray 507 has reached the initial position.

In S3080, the CPU 120 determines whether an abnormality is detected while the stack tray 507 is being raised. The processing proceeds to step S3090 when the CPU 120 determines that the abnormality is detected, and proceeds to step S3060 when the CPU 120 determines that the abnormality is not detected. The abnormality is detected in step S3080 in the same way as that in step S2060 described above.

In step S3090, the CPU 120 displays a service error illustrated in FIG. 9 on the operation unit 170, and the processing is terminated. In the screen illustrated in FIG. 9, a message indicating that a repair is required and a message instructing the user to call the serviceman are displayed. Furthermore, the contact information for calling the serviceman is also displayed.

Next, processing in step S1140 in FIG. 4 will be described by referring to FIG. 7.

The processing illustrated in FIG. 7 is performed when the CPU 120 determines that the abnormality is detected when the stack tray 507 is at the initial position in the processing in FIG. 4.

In step S4010, the CPU 120 first issues an instruction to stop the printing to the marking unit 320.

In step S4020, the CPU 120 displays a screen instructing the user to remove the obstacle on the operation unit 170. FIG. 11 illustrates an example of the displayed screen. In FIG. 11, a message indicating that the obstacle detection error of the stack tray 507 has occurred is displayed. The message indicating that the printing can be resumed by removing the obstacle is displayed. A cancel key 808 is a key for canceling the job with respect to which the printing has been stopped. An OK key 809 is a key pressed by the user after removing the obstacle. The CPU 120 determines that the obstacle is removed upon detecting that the OK key 809 is pressed.

In step S4030, the CPU 120 determines whether the obstacle is removed based on whether the OK key 809 is pressed. Specifically, the CPU 120 determines whether the OK key 809 illustrated in FIG. 11 is pressed by the user. The processing proceeds to step S1100 in FIG. 4 when the CPU 120 determines that the OK key 809 is pressed, and proceeds to step S4040 when the CPU 120 determines that the OK key 809 is not pressed.

In step S4040, the CPU 120 cancels the job with respect to which the printing has been stopped and deletes information on the job from the nonvolatile memory 140. Then, the processing is terminated.

A case where the processing proceeds to step S1180 from step S1170 in FIG. 4 is described below.

When the processing proceeds to step S1080 from step S1170 in FIG. 4, the CPU 120 acquires the lowering restricted position stored in the nonvolatile memory 140. The lowering restricted position is stored by the CPU 120 in the nonvolatile memory 140 in step S3030. Specifically, information for identifying the tray detection sensor 571 that has detected the stack tray 507 at the point of step S3030, among information pieces for respectively identifying tray detection sensors 571, is stored.

In step S1090, the CPU 120 determines whether the position of the stack tray 507 matches with the lowering restricted position which is the position of the tray detection sensor 571 identified by the acquired information. The processing proceeds to step S1130 when the CPU 120 determines that the positions match, and proceeds to step S1100 when the CPU 120 determines that the positions do not match.

When the processing proceeds to step S1130, the CPU 120 performs the processing described by referring to FIG. 6.

When the processing proceeds to step S1100 from step S1090, the CPU 120 determines whether the printing is completed. The processing returns to step S1020 when the CPU 120 determines that the printing is not completed, and the printing is terminated when the CPU 120 determines that the printing is completed.

In the present exemplary embodiment, the printing can be resumed when the user removes the sheet stacked on the stack tray 507 after lowering of the stack tray 507 is hindered by the obstacle. The operation of discharging the sheet can be resumed with a lower risk of breaking the stack tray 507 and the elevation motor 561 due to the load imposed when the stack tray 507 bumps on the obstacle again after the printing is resumed.

In the exemplary embodiment described above, the lowering restricted position is stored and lowering of the stack tray 507 is stopped at the lowering restricted position.

In a second exemplary embodiment, lowering of the stack tray 507 is stopped at a position higher than the lowering restricted position by a predetermined height.

The configuration of the MFP 100 is the same as that described by referring to FIGS. 1 to 3, and thus will not be described in detail. Only the difference from the first exemplary embodiment will be described.

The CPU 120 according to the present exemplary embodiment performs processing illustrated in a flowchart in FIG. 13 instead of FIG. 4. The CPU 120 performs processing illustrated in the flowchart in FIG. 13 by loading a program stored in the ROM 160 onto the RAM 150 and executing the program.

The difference from FIG. 4 is in steps S5010 and S5020.

In step S1080, the CPU 120 acquires the lowering restricted position stored in the nonvolatile memory 140, and the processing proceeds to step S5010.

In step S5010, the CPU 120 sets a position, higher than the lowering restricted position acquired in step S1080 by the predetermine height, as a new lowering restricted position, and stores the new lowering restricted position in the nonvolatile memory 140. The processing in step S5010 is performed by storing information for identifying the tray detection sensor 571 at a position one level higher above the tray detection sensor 571 identified in step S3030.

The predetermined height may be a fixed value determined in advance at the time of factory shipment, or may be changeable by the user through the operation unit 170 or an external apparatus. As an example case, the predetermined height of 10 cm is acquired from the user and the plurality of tray detection sensors 571 illustrated in FIG. 2 is arranged at an interval of 5 cm. In this case, the CPU 120 divides 10 cm by 5 cm, and specifies the tray detection sensor 571 at a position two levels higher above the tray detection sensor 571 identified by the information acquired in step S1080. Then, the CPU 120 sets the information for identifying the specified tray detection sensor 571 as the new lowering restricted position.

In step S5020, the CPU 120 determines whether the position of the stack tray 507 matches with the lowering restricted position which is the position of the tray detection sensor 571 identified by the information set in step S5010. The processing proceeds to step S1130 when the CPU 120 determines that the positions match, and proceeds to step S1100 when the CPU 120 determines that the positions do not match.

When the processing proceeds to step S1130, the CPU 120 performs the processing described by referring to FIG. 6.

When the processing proceeds to step S1100 from step S1090, the CPU 120 determines whether the printing is completed. The processing returns to step S1020 when the CPU 120 determines that the printing is not completed, and is terminated when the CPU 120 determines that the printing is completed.

Through the control described above, the user can resume the printing by removing the sheet stacked on the stack tray 507 after lowering of the stack tray 507 is hindered by the obstacle. After the printing is resumed, the operation of discharging the sheet can be resumed, lowering a risk of bringing the stack tray 507 into contact with the obstacle again.

Furthermore, the predetermined height is changeable by the user. Thus, the user can increase the predetermined height to reduce the risk of bringing the stack tray 507 into contact with the obstacle, and can reduce the predetermined height to increase the number of stackable sheets.

Other Exemplary Embodiment

In the exemplary embodiments described above, the example where the height of the stack tray 507 is detected by the tray detection sensor 571 is described. A method for detecting the height of the stack tray 507 is not limited to this. For example, a sensor that counts projection portions of the concavity and convexity of the belt 554 for raising and lowering the stack tray 507 may be used. In this case, the CPU 120 may recognize the position of the stack tray 507 based on the number of the projection portions counted from the initial position of the stack tray 507. For example, the projection portions of the concavity and convexity are disposed at an interval of 5 mm. In this case, when 50 projection portions are counted from the initial position, the CPU 120 recognizes that the stack tray 507 is at a position 250 mm lower from the initial position. When this method is employed, the position of the stack tray 507 at the point where the obstacle is detected is stored as X mm. The operation of lowering the stack tray 507 may be stopped at X mm after the printing and the stacking are resumed. The lowering of the stack tray 507 may be stopped at Y mm obtained by subtracting X mm by a predetermined height. The predetermined height may be a fixed value such as 5 cm or 10 cm determined in advance at the time of factory shipment, or may be changeable by the user through the operation unit 170 or an external apparatus. Alternatively, the CPU 120 may recognize the number of rotations of the elevation motor 561 for raising and lowering the stack tray 507, and detect the height of the stack tray 507 based on the number of rotations thus recognized.

Other Embodiments

Embodiments of the present invention can also be realized by a computer of a system or apparatus that reads out and executes computer executable instructions recorded on a storage medium (e.g., non-transitory computer-readable storage medium) to perform the functions of one or more of the above-described embodiment(s) of the present invention, and by a method performed by the computer of the system or apparatus by, for example, reading out and executing the computer executable instructions from the storage medium to perform the functions of one or more of the above-described embodiment(s). The computer may comprise one or more of a central processing unit (CPU), micro processing unit (MPU), or other circuitry, and may include a network of separate computers or separate computer processors. The computer executable instructions may be provided to the computer, for example, from a network or the storage medium. The storage medium may include, for example, one or more of a hard disk, a random-access memory (RAM), a read only memory (ROM), a storage of distributed computing systems, an optical disk (such as a compact disc (CD), digital versatile disc (DVD), or Blu-ray Disc (BD)™), a flash memory device, a memory card, and the like.

While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.

This application claims the benefit of Japanese Patent Application No. 2013-248040 filed Nov. 29, 2013, which is hereby incorporated by reference herein in its entirety. 

What is claimed is:
 1. A sheet stacking apparatus comprising: a lowering control unit configured to lower a sheet stacking unit according to an amount of a sheet that is stacked; a determination unit configured to determine that the sheet stacking unit cannot be lowered by the lowering control unit; and a control unit configured to perform control to store a position of the sheet stacking unit in a storage unit and stop stacking of the sheet on the sheet stacking unit when the determination unit determines that the sheet stacking unit cannot be lowered while the sheet is being stacked on the sheet stacking unit, wherein the control unit is configured to perform control to raise the sheet stacking unit when the sheet stacked on the sheet stacking unit is removed in a state where the stacking of the sheet on the sheet stacking unit is stopped, stack the sheet on the raised sheet stacking unit, and stop lowering of the sheet stacking unit based on the position stored in the storage unit.
 2. The sheet stacking apparatus according to claim 1, wherein the control unit is configured to perform control to raise the sheet stacking unit when the sheet stacked on the sheet stacking unit is removed, stack the sheet on the raised sheet stacking unit, and stop lowering of the sheet stacking unit at the position stored in the storage unit.
 3. The sheet stacking apparatus according to claim 1, wherein the control unit is configured to perform control to raise the sheet stacking unit when the sheet stacked on the sheet stacking unit is removed, stack the sheet on the raised sheet stacking unit, and stop lowering of the sheet stacking unit at a position higher than the position stored in the storage unit.
 4. The sheet stacking apparatus according to claim 1, wherein the control unit is configured to perform control to resume the stacking of the sheet on the sheet stacking unit when an obstacle placed below the sheet stacking unit is removed in the state where the stacking of the sheet on the sheet stacking unit is stopped, and wherein the lowering control unit is configured to lower the sheet stacking unit from the position at which the stacking of the sheet is stopped, instead of the control unit performing control to raise the sheet stacking unit.
 5. The sheet stacking apparatus according to claim 1, wherein the control unit is configured to cancel a job for stacking the sheet, when an instruction to cancel the job for stacking the sheet is received in the state where the stacking of the sheet on the sheet stacking unit is stopped.
 6. The sheet stacking apparatus according to claim 1, further comprising a notification unit configured to instruct removal of the sheet stacked on the sheet stacking unit or the obstacle placed below the sheet stacking unit when the determination unit determines that the sheet stacking unit cannot be lowered while the stacking of the sheet on the sheet stacking unit is being performed.
 7. The sheet stacking apparatus according to claim 1, wherein the control unit is configured to perform control to display, on a display unit, a screen for calling a serviceman when the sheet stacking unit cannot be raised while the sheet stacking unit is being raised after the sheet stacked on the sheet stacking unit is removed.
 8. The sheet stacking apparatus according to claim 1, further comprising a printing unit configured to print an image onto the sheet, wherein the sheet on which the image is printed by the printing unit is stacked on the sheet stacking unit.
 9. The sheet stacking apparatus according to claim 8, further comprising a read unit configured to read an image on a document, wherein the printing unit is configured to print the image read by the read unit.
 10. A sheet stacking apparatus comprising: a lowering control unit configured to lower a sheet stacking unit according to an amount of a sheet that is stacked; a determination unit configured to determine that the sheet stacking unit cannot be lowered by the lowering control unit; and a control unit configured to perform control to stop stacking of the sheet on the sheet stacking unit at a first position at which the determination unit has determined that the sheet stacking unit cannot be lowered while the sheet is being stacked on the sheet stacking unit, wherein the control unit is configured to perform control to raise the sheet stacking unit when the sheet stacked on the sheet stacking unit is removed in a state where the stacking of the sheet on the sheet stacking unit is stopped at the first position, stack the sheet on the raised sheet stacking unit, and stop lowering of the sheet stacking unit at a second position that is higher than the first position by a predetermined height.
 11. The sheet stacking apparatus according to claim 10, further comprising a reception unit configured to receive the predetermined height from a user.
 12. A sheet stacking apparatus comprising: a lowering control unit configured to lower a sheet stacking unit to a lowermost position according to an amount of a sheet that is stacked; a determination unit configured to determine that the sheet stacking unit cannot be lowered by the lowering control unit at a first position that is different from the lowermost position; and a control unit configured to perform control to stop stacking of the sheet on the sheet stacking unit at the first position at which the determination unit has determined that the sheet stacking unit cannot be lowered while the sheet is being stacked on the sheet stacking unit, wherein the control unit is configured to perform control to raise the sheet stacking unit when the sheet stacked on the sheet stacking unit is removed in a state where the stacking of the sheet on the sheet stacking unit is stopped at the first position, stack the sheet on the raised sheet stacking unit, and stop lowering of the sheet stacking unit at the first position.
 13. A method for controlling a sheet stacking apparatus having a lowering control unit configured to lower a sheet stacking unit according to an amount of a sheet that is stacked and a determination unit configured to determine that the sheet stacking unit cannot be lowered by the lowering control unit, the method comprising: performing control to store a position of the sheet stacking unit in a storage unit and stop stacking of the sheet on the sheet stacking unit when the determination unit determines that the sheet stacking unit cannot be lowered while the sheet is being stacked on the sheet stacking unit; and performing control to raise the sheet stacking unit when the sheet stacked on the sheet stacking unit is removed in a state where the stacking of the sheet on the sheet stacking unit is stopped, stack the sheet on the raised sheet stacking unit, and stop lowering of the sheet stacking unit based on the position stored in the storage unit.
 14. A computer readable storage unit storing a program to cause a computer to execute a method for controlling a sheet stacking apparatus having a lowering control unit configured to lower a sheet stacking unit according to an amount of a sheet that is stacked and a determination unit configured to determine that the sheet stacking unit cannot be lowered by the lowering control unit, the method comprising: performing control to store a position of the sheet stacking unit in a storage unit and stop stacking of the sheet on the sheet stacking unit when the determination unit determines that the sheet stacking unit cannot be lowered while the sheet is being stacked on the sheet stacking unit; and performing control to raise the sheet stacking unit when the sheet stacked on the sheet stacking unit is removed in a state where the stacking of the sheet on the sheet stacking unit is stopped, stack the sheet on the raised sheet stacking unit, and stop lowering of the sheet stacking unit based on the position stored in the storage unit. 